Dynamic estimation of an active surgical needle deflection for brachytherapy procedures

In this study, we present the dynamic response of a shape memory alloy (SMA) actuated steerable needle. The active needle can be used in many diagnostic and therapeutic percutaneous needle-based procedures. For instance brachytherapy, one the most popular prostate cancer treatments, could greatly benefit from the active needle for accurate placement of radioactive seed in target locations. In order to show the real-time deflection of the active needle under actuation of SMA wires both finite element analyses (FEA) and prototype experimentation methods were utilized. Prediction of the complex stress-strain response of SMAs due to their internal phase transformation was a challenging part of this study. Rigorous experiments were done to determine the SMA´s material properties and to show a stabilized SMA transformation behavior with sufficient accuracy. A three-dimensional FE model of the active steerable needle was developed in ANSYS to demonstrate the feasibility of using SMA wires as actuators to bend the surgical needle. The birth and death method was used to achieve the pre-strain condition on SMA wire prior to actuation. This numerical simulation was validated with needle deflection experiments with developed prototypes of the active needle. Real-time experiments with different prototypes showed that the quickest response and the maximum deflection were achieved by the needle with multiple actuation sections.